The initiation of labour

The onset of labour involves progesterone withdrawal and increases in oestrogen and prostaglandin action. The mechanisms that regulate these changes are unresolved but likely involve placental production of the peptide hormone corticotrophin-releasing hormone (CRH).

During pregnancy, painless irregular uterine activity is present. It is minimal in early pregnancy and greater with advancing gestation. There is a cascade of events regulated and controlled by the fetoplacental unit. At the end of gestation, there is gradual downregulation of those factors that keep the uterus and cervix quiescent and an upregulation of procontractile influences.

Placental development across gestation leads to an exponential increase in the number of syncytiotrophoblast nuclei in which transcription of the CRH gene occurs. This maturational process leads to an exponential increase in the levels of maternal and fetal plasma CRH. The CRH has direct actions on the placenta to increase oestrogen synthesis and reduce progesterone synthesis. In the fetus the CRH directly stimulates the fetal zone of the adrenal gland to produce dehydroepiandrosterone (DHEA) the precursor of placental oestrogen synthesis. CRH also stimulates the synthesis of prostaglandins by the membranes. The fall in progesterone and increase in oestrogens and prostaglandins leads to increases in connexin 43 that promotes connectivity of uterine myocytes and changes uterine myocyte electrical excitability, which in turn leads to increases in generalized uterine contractions:

The integrity of the cervix is essential to retain the products of conception. It contains myocytes and fibroblasts, and towards term becomes soft and stretchable due to an increase in leucocyte infiltration and a decrease in the amount of collagen with the increase in proteolytic enzyme activity. Increased production of hyaluronic acid reduces the affinity of fibronectin for collagen. The affinity of hyaluronic acid for water causes the cervix to become soft and stretchable, i.e. ripening of the cervix.

Reduced cervical resistance (i.e. release of the brakes in a car) and increasing frequency, duration and strength of uterine contractions (i.e. accelerator of the car) are needed for the progress of labour. The first stage of labour that starts from onset of painful uterine contractions to full dilatation is divided into a slow latent phase when the cervix becomes shorter, i.e. effaced and dilated to 3–4 cm (an average of 6-8 hours in nulliparae and 4-6 hours in a multiparae) and an active phase of labour when the cervix dilates at an average of 1 cm per hour from 3–4 cm to full cervical dilatation.

Examination at the commencement of labour

On admission, the following examination should be performed:

The following factors should be noted:

In vertex presentation the degree of caput (soft tissue scalp swelling), moulding (0, +1. +2 and +3) and synclitism (sagittal suture bisects the pelvis) should be noted.

General principles of the management of the first stage of labour

The guiding principles of management are:

Observation: the use of the partogram

The introduction of graphic records of progress of cervical dilatation and descent of the head was a major advance in the management of labour. It enables the early recognition of a labour that is non-progressive. The partogram (Fig. 11.6) is a single sheet of paper on which there is a graphic representation of progress in labour. On the same sheet other observations related to labour can be entered. There are sections to enter the frequency and duration of contractions, fetal heart rate (FHR), colour of liquor, caput and moulding, station or descent of the head, maternal heart rate, BP and temperature. The partogram should be started as soon as the mother is admitted to the delivery suite and this is recorded as zero time regardless of the time at which contractions started. However, the point of entry on to the partogram depends on a vaginal assessment at the time of admission to the delivery suite. The value of this type of record system is that it draws attention visually to any aberration from normal progress in labour.

The use of partograms at an applied level was first introduced in remote obstetric units in Africa, where recognition that progress in labour is becoming abnormal enables early transfer to specialist units before serious obstruction occurs.

This has led to a major reduction in maternal mortality due to avoidance of uterine rupture, sepsis and postpartum haemorrhage and reduction in severe morbidity of vesico or recto vaginal fistula. Earlier recognition of obstructed labours and immediate attention by caesarean delivery where indicated prevents such tragedies.

Narcotic analgesia

Pethidine has traditionally been the most widely used narcotic agent but has been replaced in many centres in the UK and Australia by morphine. The common side effects for all the opiates are nausea and vomiting in the mother and respiratory depression in the baby. The effect on the neonate is particularly important when the drug is given within 2 hours of delivery. Opiates are often administered with anti-emetics to reduce nausea.

Remifentanil is used in some centres as this is an ultra-short-acting opioid that produces superior analgesia to pethidine and has less of an effect on neonatal respiration.

Because some mothers are unsuitable for regional analgesia, e.g. those on anticonvulsants, opiates are likely to continue to play a significant role in pain relief in labour.

Inhalational analgesia

These agents are used in early labour until the mother switches to much stronger analgesics. It is best for short-term pain relief in the late first and second stage of labour. The most widely used agent is entonox, which is a 50/50 mixture of nitrous oxide and oxygen. The gas is self-administered to avoid overdosing when they drop the mask off and is inhaled as soon as the contraction starts. Entonox is the most widely used analgesic in labour in the UK and provides sufficient pain relief for the majority.

Nitrous oxide has been shown to have adverse effects on birth attendants if exposure is prolonged; these effects include decreased fertility, bone marrow changes and neurological changes. Forced air change every 6–10 hours is effective in reducing the nitrous oxide levels and should be mandatory in all delivery rooms.

Non-pharmacological methods

Transcutaneous electrical nerve stimulation (TENS) involves the placement of two pairs of TENS electrodes on the back on each side of the vertebral column at the levels of T10–L1 and S2–S4. Currents of 0–40 mA are applied at a frequency of 40–150 Hz. This can be effective in early labour but is often inadequate by itself in late labour. For the technique to be effective, antenatal training of the mother is essential.

Other non-invasive methods include acupuncture, subcutaneous sterile water injections, massage and relaxation techniques: the effectiveness of which are debated.

Regional analgesia

Epidural analgesia is the most effective and widely used form of regional analgesia. It provides complete relief of pain in 95% of labouring women.

The procedure may be instituted at any time and does not interfere with uterine contractility. It may reduce the desire to bear down in the second stage of labour due to lack of pressure sensation at the perineum and reduced uterine activity due to loss of ‘Ferguson reflex’: which is an increased uterine activity due to reflex release of oxytocin due to the presenting part stretching the cervix and upper vagina.

A fine catheter is introduced into the lumbar epidural space and a local anaesthetic agent such as bupivacaine is injected (Fig. 11.7). The addition of an opioid to the local anaesthetic greatly reduces the dose requirement of bupivacaine, thus sparing the motor fibres to the lower limbs and reducing the classic complications of hypotension and abnormal fetal heart rate.

The procedure involves:

The complications of epidural analgesia include:

Contraindications to regional anaesthesia include:

Other forms of regional anaesthesia

Spinal anaesthesia is commonly used for operative delivery, particularly as a single-shot procedure. It is not used for control of pain in labour because of the superior safety of epidural analgesia and the ability to top up with suitable doses or as continuous infusion to get pain relief over a long period of time.

Paracervical blockade involves the infiltration of local anaesthetic agents into the paracervical tissues. This is rarely used for obstetric procedures and has the greater chance of side effects to the fetus should it enter a vessel.

Pudendal nerve blockade involves infiltration around the pudendal nerve as it leaves the pudendal canal and the inferior haemorrhoidal nerve (Fig. 11.8). It was a widely used form of local anaesthesia for operative vaginal deliveries in the past but is now less frequently used as it has been replaced by epidural anaesthesia.

Infiltration directly into the perineal tissues over the episiotomy site is still widely used for the repair of perineal wounds. Great care must be taken to avoid direct intravenous injection of the drug at the time of local infiltration. Toxic symptoms such as cardiac arrhythmias and convulsions may result from accidental injection of the anaesthetic drug especially with larger dosage.

Water births

Some mothers prefer immersion in a water bath for pain relief. Flotation improves support of the pregnant uterus. Most women prefer to deliver outside water. There is a possibility of the baby inhaling the bath water with the first breath which can cause problems to the baby if the bath is contaminated with maternal faeces. The temperature of the bath has to be regularly checked and mother should not be left alone in the water bath.

Intermittent auscultation

During labour, the FHR is monitored every 15 minutes for a period of 1 minute soon after a contraction using a handheld Doppler ultrasound transducer or pinard fetal stethoscope in the first stage of labour. In the second stage the FHR is auscultated every 5 minutes or every other contraction. Contractions are monitored by manual palpation over a period of 10 minutes to determine the frequency and duration. The frequency of intermittent auscultation (IA) was recommended on the basis that there was no difference in fetal and neonatal outcome in randomized studies that compared IA every 15 minutes for 1 minute after a contraction in the first stage and every 5 minutes in the second stage with EFM.

The clinical guidelines for the use of electronic fetal monitoring have been produced by the Royal College of Obstetricians and Gynaecologists in the UK and Australia and New Zealand and by similar bodies in USA and Canada as well as by the National Institute for Health and Clinical Excellence in the UK. They have great similarities and minor differences that are unlikely to influence clinical outcome. Admission cardiotocogram or routine CTG using electronic monitoring is not recommended for women classified as low risk. The specific indications for continuous electronic fetal monitoring are listed in Table 11.1.

Basal heart rate

The definition of normality in the pattern of the fetal heart rate is easier than defining what is abnormal. The normal heart rate varies between 110 and 160 beats/min (Fig. 11.10). A rate faster than 160 is defined as fetal tachycardia and a rate less than 110 is fetal bradycardia.

Transient changes in fetal heart rate (Tables 11.2 and 11.3)

There are a number of factors known to be associated with spontaneous preterm labour, although in many cases the cause is unknown.

Some of the major factors associated with the preterm labour are shown in Figure 11.11. There is an association with poor social conditions and nutritional status and also with antepartum haemorrhage, multiple pregnancy, uterine anomalies, cervical incompetence and PROM, which is often associated with infection. A previous history of preterm delivery is the best single predictor. The relative risk is about 3 and the risk increases if there has been more than one preterm delivery. Complications during a pregnancy may also precipitate preterm labour; this includes over distension of the uterus, such as multiple pregnancy and hydramnios. Other factors, such as haemorrhage in either the first or early second trimester, increase the risk of subsequent preterm labour. Severe maternal illness, particularly febrile illness, may also promote the early onset of labour.

Social factors involve maternal age (under 20 or over 35 years), primiparity, ethnicity, marital status, cigarette smoking, substance abuse and heavy, stressful work (Box 11.1). Active social intervention appeared to reduce the incidence of preterm labour in early studies but has not received unanimous support due to lack of good scientific evidence.

If the cause is of infective origin it may affect the mother but the effect is predominantly on the fetus. Improvements in neonatal services provide good chance of intact survival if the new born is in good condition and is of reasonable birth weight. Each day of delay in birth after 24 weeks increases the chance of survival by 3–6%, and hence the need to conserve the pregnancy as long as possible. An infant born with a birth weight of less than 500 g has little chance of survival whereas one born weighing 1500 g is nearly as likely to survive as a full-term infant. Between 500 and 1000 g, every 100 g increment produces a significant increase in survival (Fig. 11.12). The major causes of death in very-low-birth weight infants are infection, respiratory distress syndrome, necrotizing enterocolitis and periventricular haemorrhage.

The management of preterm labour

The diagnosis of preterm labour is based on the onset of regular uterine contractions associated with progressive cervical effacement and dilatation. Uterine contractions are a common and normal occurrence during pregnancy and do not always progress to established labour. Over 30% of hospital admissions for suspected preterm labour may be discharged home undelivered. The presence of the protein fetal fibronectin in the cervix can be used in the assessment of the risk of preterm delivery. The test can be performed by taking a swab from the cervix provided that the membranes are intact and the woman has not had intercourse or a vaginal examination within the previous 24 hours. A negative result makes delivery within the next 7 days unlikely (<3%) although a positive test result is of less value as only 20% of such women will deliver in the same period.

Treatment

Once the woman is admitted to hospital in established preterm labour, a decision must be made as to the approach to management. The long-term advantages of preventing preterm labour are uncertain, although every day of delay in the early preterm period increases the chance of survival and reduces morbidity and more dependence on intensive care. There is no controversy in postponing delivery long enough for the administration of corticosteroids to enable the production of fetal lung surfactant with the aim of reducing the chance of hyaline membrane disease (HMD) and respiratory distress syndrome (RDS) (Fig. 11.13).

The decision whether labour should be allowed to proceed or to inhibit uterine activity depends on the period of gestation, absence of infection or bleeding, intact membranes and the cervix being less than 5 cm dilated. In cases where gestational age by ultrasound dating is less than 34 weeks, it is appropriate to inhibit uterine activity pharmacologically until corticosteroids can be administered to the mother.

Tocolysis is contraindicated in the presence of bleeding because of the risk of maternal haemodynamic compromise and with infection as delay may compromise the health of mother and fetus.

Drug therapy to delay the delivery can be divided into groups operating on different principles (Box 11.2).

Box 11.2   Drug treatment for preterm labour

• β-Adrenergic agonists

• Prostaglandin synthetase inhibitors

• Magnesium sulphate

• Slow calcium-channel blockers

• Corticosteroids

• Oxytocin antagonists

β-Adrenergic agonists

These drugs act on the β-2-adrenergic receptor sites on the membranes of the myometrial cells, with the activation of adenyl cyclase resulting in an increase in intracellular cyclic adenosine monophosphate (cAMP). Action is by inhibition of actin–myosin interaction, which inhibits uterine activity.

These drugs have potentially dangerous maternal side effects and hence must be used with caution. The side effects include palpitations and tremor, ischaemic arrhythmias, pulmonary oedema and sometimes sudden death.

The most commonly used drugs are ritodrine, salbutamol and terbutaline. The drugs should not be used where there is a known history of cardiovascular disease and hypertension.

The drugs are administered diluted in 5% dextrose or dextrose/saline and the infusion rate should be incrementally increased every 10–20 minutes until contractions are reduced to one every 15 minutes, or until the maternal heart rate has reached 140 beats/min. Careful monitoring of maternal pulse rate, blood pressure, urinary output and plasma electrolytes is essential. Fluid overload due to IV fluids and drug action increasing antiduretic hormone causing retention of fluids is the main cause of pulmonary oedema and heat failure and this may be greater in multiple pregnancy.

β-adrenergic drugs can cause hypokalaemia, hyperglycaemia (ketoacidosis in diabetics) and pulmonary oedema with prolonged use.

The dosage can be reduced slowly after the administration of corticosteroids to the mother. It is unlikely that any major benefit will accrue to the fetus if the gestational age exceeds 34 weeks. It is necessary to continue treatment till the mother is transferred to a tertiary care centre with neonatal intensive care facilities. Oral maintenance therapy remains unproven and is not recommended.

Prostaglandin synthetase inhibitors

Drugs such as indocid (indomethacin) given at a dose of 1–3 mg/kg maternal body weight for 24 hours inhibit prostaglandin production and thus uterine activity. These drugs are very effective in preventing the progression of labour. However, they also result in in utero closure of the ductus arteriosus and may therefore adversely affect the fetal circulation. There may be occasions when they are the drug of choice and where the preterm delivery of the infant constitutes a greater risk than the not invariable early closure of the ductus. This drug also increases pulmonary and renal artery resistance and can cause oligohydramnios. Such consequences are best avoided by using the drug for 1-3 days at the minimum required dose. Usually it is given as 100 mg suppositories.

Indomethacin also reduces liquor volume by its effect on fetal renal function, so may be of additional benefit in cases of polyhydramnios.

Calcium antagonists

The effect of slow calcium channel blockers in inhibiting uterine activity is not in doubt. There has been some evidence in animal studies using very large doses of these compounds, in particular nifedipine, that they may cause rib fusions in the fetus if given during the period of organogenesis. However, if the drugs are administered in the late second and third trimesters, this is well past this period and there is no evidence that they pose a threat.

Nifedipine is administered with a starting oral dose of 20 mg followed by 10–20 mg every 4–6 hours thereafter. Severe side effects are rare.

Calcium antagonists, although not licensed for use in pregnancy in the UK, are recommended by the Royal College of Obstetricians and Gynaecologists as the drug of choice to inhibit the uterine activity because of its efficacy and low cost.

Corticosteroids

The use of corticosteroids in the prevention of respiratory distress is based on the action of these compounds in enhancing the production of surfactant, thus enabling rapid expansion of the alveoli at the time of delivery and the establishment of normal respiratory function. Controlled trials on the antenatal effects of corticosteroids in preterm infants have shown that there are significant reductions in respiratory distress syndrome, periventricular haemorrhage and necrotizing enterocolitis.

The dosage of betamethasone or dexamethasone is given on the basis of 12 mg 12-hourly by intramuscular injection on two occasions. Optimal benefit can be achieved if delivery is postponed for at least 24 hours and up to 7 days. Over 34 weeks gestation, the administration of corticosteroids is not justified. The production of phosphatidylcholine can also be enhanced by the administration of thyrotrophin-releasing hormone (TRH) to the mother.

Failure to prescribe corticosteroids before delivery between 28 and 34 weeks may now be considered to be negligent.

Neuroprotection by magnesium sulphate

The use of magnesium sulphate as a tocolytic has largely been abandoned because of its low efficacy. However, large randomized studies have shown a neuroprotective effect in the neonate with its use prior to preterm delivery. It stabilizes capillary membranes and reduces the incidence of intra and periventricular haemorrhage. An IV dose of 4 g MgSO₄ is given followed by 1 g every hour for the next 24 hours. However, there is a trial that suggests that even a bolus dose of 4 g without subsequent continued dose is effective and offers neuroprotection after 24 hours. There is little information available as to whether this regime could be repeated if the delivery does not ensue and the mother restarts in preterm labour. A pragmatic approach is to give another dose if the interval was greater than one week.

Pathogenesis

Prelabour rupture of the membranes has no known major risk factor but is associated with first and second trimester haemorrhage and, less predictably, with smoking. However, the most common factor is infection. Various organisms have been described in this context; these include group B haemolytic streptococci, C. trachomatis and those organisms causing bacterial vaginosis.

Management

The mother will come with a history of sudden loss of amniotic fluid from her vagina. On admission to hospital, a speculum examination should be performed to confirm the presence of amniotic fluid, although sometimes it can be difficult to confirm the diagnosis. The use of nitrazine sticks is of limited value and tests using more specific markers based on the presence of α-fetoprotein and insulin-like growth factor (IGF) are not widely used because of their cost.

The risks to the mother and baby are those of infection. However, long-term drainage of amniotic fluid may result in fetal pulmonary hypoplasia. The difficulty is to decide both when to deliver the fetus and how to effect delivery, as the uterus may not respond adequately to the action of oxytocic agents especially in the very preterm period.

Where there is doubt, it is better to continue observation to look for wetness of a sanitary pad worn to assist in the diagnosis. An ultrasound examination that shows the presence of normal quantities of amniotic fluid with a pocket of fluid between the presenting part and the cervix with no fluid escaping into the vagina is highly suggestive of intact membranes.

If there is clear evidence of amniotic fluid in the vagina, swabs should be taken for culture. Maternal infection may result in uterine tenderness, fetal and/or maternal tachycardia and pyrexia as well as the presence of a purulent vaginal discharge. Monitoring for the presence of maternal sepsis is best performed by the measurement of blood white cell count and C-reactive protein (CRP). Increasing levels of CRP on subsequent estimations suggest the presence of infection.

If there is a positive culture or evidence of maternal infection, the appropriate antibiotic should be administered. If there is evidence of infection, labour should be induced using an oxytocic infusion and delivery expected in the interest of the fetus and the mother. If there is no evidence of infection, conservative management with erythromycin cover should be adopted. Tocolysis is generally ineffective in the presence of ruptured membranes if contractions are already well established and one should consider whether the underlying triggering factor may be infection. If gestation is over 28 weeks the infant probably has a better chance of survival if delivered. Most women with PROM will deliver spontaneously within 48 hours.

At term, women with PROM are induced with prostaglandins or syntocinon on admission or after 24 hours of PROM. In the preterm period conservative management is adopted with the warning that there may be risks of infection, abruption, cord prolapse, pulmonary hypoplasia or stillbirth but the need for conservatism to advance to a mature gestation for better survival and outcome.

Indications

The major indications for induction of labour are:

Prolonged pregnancy is defined as pregnancy exceeding 294 days from the first day of the last menstrual period in a woman with a 28-day cycle. The perinatal mortality rate doubles after 42 weeks and trebles after 43 weeks compared with 40 weeks gestation. Although, routine induction of labour has a minimal effect on the overall perinatal mortality rate, it is offered after 41+ weeks as an adverse outcome is not an acceptable option for the individual mother. Conservative management of prolonged pregnancy is preferred by some and it involves at least twice weekly monitoring of the fetus with ultrasound assessment of liquor volume and non-stress test (NST) or antenatal CTG. Induction is undertaken if there is suspicion of fetoplacental compromise. However, many women request induction of labour on the basis of the physical discomfort of the continuing pregnancy. The chance of successful vaginal delivery should be considered and explained to the mother based on parity and cervical score. Artificial separation of membranes just past 40 weeks reduces the number who may need induction after 41 weeks.

Cervical assessment

Clinical assessment of the cervix enables prediction of the likely outcome of induction of labour. The most commonly used method of assessment is the Bishop score or by modification of this score. This cervical score involves clinical examination of the cervix.

A Bishop score of more than 6 is strongly predictive of labour following induction. A score of less than 5 indicates the need for cervical ripening.

Methods of induction

The method of induction will be determined by whether membranes are still intact and the score on cervical assessment.

Forewater rupture

Rupture of the membranes should be performed under conditions of full asepsis in the delivery suite. Under ideal circumstances, the cervix should be soft, effaced and at least 2 cm dilated. The head should be presenting by the vertex and should be engaged in the pelvis. In practice, these conditions are often not fulfilled, and the degree to which they are adhered to depends on the urgency of the need to start labour. The mother is placed in the supine or lithotomy position and, after swabbing and draping the vulva, a finger is introduced through the cervix, and the fetal membranes are separated from the lower segment: a process known as ‘stripping the membranes’. The bulging membranes are then ruptured with Kocher’s forceps, Gelder’s forewater amniotomy forceps or an amniotomy hook (Fig. 11.14). The amniotic fluid is released slowly and care is taken to exclude presentation or prolapse of the cord. The fetal heart rate should be monitored for 30 minutes before and following rupture of the membranes.

Hindwater rupture

An alternative method of surgical induction involves rupture of the membranes behind the presenting part. This is known as hindwater rupture. A sigmoid-shaped metal cannula known as the Drewe–Smythe catheter is introduced through the cervix and penetrates the membranes behind the presenting part (Fig. 11.15). The theoretical advantage of this technique is that it reduces the risk of prolapsed cord. In reality, the risk is even lower with forewater rupture than with spontaneous rupture of the membranes, and the technique of hindwater rupture is now rarely used.

Uterine hyperstimulation

The commonest contemporary cause of uterine hyperstimulation is the uncontrolled use of excessive amounts of oxytocic drugs. In extreme cases, this may result in uterine tetany with a continuous contraction. Leading up to this state, there will be frequent strong contractions and insufficient time between contractions to allow a return to normal baseline pressures. The condition can be rapidly corrected by turning off the oxytocin infusion. In fact, the condition should not arise if uterine activity is properly monitored by external or internal tocography. Contractions should not occur more frequently than five in 10 minutes. Greater than 5 contractions in 10 minutes affect the placental perfusion and oxygenation of the fetus. Hyperstimulation (>5 contractions in 10 minutes) associated with FHR changes is termed ‘hyperstimulation syndrome’ (National Institute for Health and Clinical Excellence).

The uterus becomes more and more sensitive to the same dose of oxytocin with advance in labour and greater cervical dilatation and hence it is important to carefully monitor the contractions and reduce or stop the oxytocin infusion should the contraction frequency increases to >5 in 10 minutes.

Uterine hyperstimulation can occur with the use of prostaglandins in various forms. This is due to rapid absorption of the drug from the vagina as the rate of absorption is affected by the temperature and pH of the vagina and the presence of infection/inflammation. This is best managed by removal of the PG pessary and the use of a bolus dose of a short acting tocolytic such as 0.25 mg terbutaline as SC or in 5 mL saline as a slow IV.

Hyperstimulation may also lead to uterine rupture, particularly where there is a uterine scar from a previous section or myomectomy. Such a rupture may sometimes occur even in the presence of normal uterine activity.

Hypotonic uterine activity

In this condition, the resting uterine tone is low, contractions are infrequent and often irregular, and progress is slow. This type of inertia results in delays in the latent phase and does not usually cause distress to the mother or the fetus.

Hypertonic uterine activity

This is a rare abnormality commonly resulting from reversed polarity of the uterine contractions. The contraction is commonly initiated in the lower segment or it may on occasions be asymmetrical, resulting in a double peak in the contraction wave. Resting uterine tone is also raised so that the level at which the pain of the contraction is felt is earlier in the contraction cycle and the pain persists for longer. Cervical dilatation is slow and the woman suffers from severe backache and pain that radiates into the lower abdomen. This type of inertia is uncommon and, when it does occur, is commonly associated with placental abruption. This diagnosis must always be considered when this type of labour occurs as the abruption may initially be concealed.

   Case study

A 23-year-old primigravida was admitted to hospital in labour with regular and painful contractions. There was no evidence of any antepartum haemorrhage. The cervix was found to be 2.5 cm dilated. However, 4 hours later the cervix was 4 cm dilated and the rate of progress was significantly delayed. The cervicogram is shown in Figure 11.16. An epidural catheter was inserted and epidural analgesia commenced. The membranes were ruptured artificially and clear amniotic fluid was released. Progress in labour continued to be slow and 3 hours later a dilute oxytocin infusion was started. This resulted in rapid progress to full dilatation and vaginal delivery some 2 hours later.

Management

Abnormalities of uterine activity are usually recognized by the failure of progress in labour. As incoordinate uterine activity may also be associated with cephalopelvic disproportion, it is essential to exclude this possibility by careful assessment of the size and shape of the maternal pelvis and the size of the fetus.

The general principles of management of abnormal uterine activity involve:

In the presence of hypotonic uterine inertia, uterine activity may be stimulated by encouraging mobilization of the mother and, if the membranes are intact, by artificial rupture of the membranes; an oxytocic infusion will also usually stimulate labour and delivery.

If the uterine activity is hypertonic, rupture of the membranes as well as cautious use of a low-dose oxytocin infusion may produce normal uterine activity. If progress continues to be slow and there is evidence of fetal distress, delivery should be effected by caesarean section.

Constriction ring dystocia can only be reversed by the use of beta-sympathomimetic agents, or ether or halothane anaesthesia.

Management

When the possibility of cephalopelvic disproportion is suspected, labour should be carefully monitored. Regular observations must be recorded of uterine activity, the rate of cervical dilatation, the descent of the presenting part, the position, station and the caput and moulding and the condition of both the mother and the fetus.

In primigravid women, the uterus may become exhausted late in the first stage and contractions may cease or become attenuated and there may be no progress in cervical dilatation. If there is no change in cervical dilatation over a period of 4–6 hours, with no descent of head, increasing caput and moulding, the trial of labour should be abandoned. Similarly, if clinical signs of fetal distress or maternal exhaustion develop, the labour should be terminated by caesarean section.

   Case study

A 38-year-old multigravid woman was admitted in labour at term. After good initial progress in labour, significant arrest occurred at 8 cm dilatation (Fig. 11.17). Vaginal examination confirmed the presence of an occipitoposterior position associated with marginal cephalopelvic disproportion. The cervix eventually became fully dilated and the head was rotated and delivered with forceps.

Predisposing factors

Any condition that displaces the head or presenting part away from the cervix or where the presenting part is irregular and forms poor contact with the cervix will predispose to cord presentation or prolapse. Under these circumstances, if the membranes are ruptured artificially to induce labour, the cord may prolapse. In normal labour the uterine contractions are likely to cause descent of the presenting part and fix it to the pelvic brim and spontaneous rupture of membranes is much later in labour. With artificial rupture of membranes for induction of labour the head may be higher with slightly increased incidence of cord prolapse but because the patient will be near an operating theatre the baby can be delivered rapidly.

Management

The diagnosis of cord presentation is sometimes made prior to rupture of the membranes and prolapse of the cord but this is the exception rather than the rule. If the cord prolapses through a partially dilated cervix, delivery should be effected as soon as possible, as the presenting part will compress the cord or the cord arteries may go into spasm on exposure to cold air. Handling of the cord may cause the same effect. Cord spasm or compression leads to fetal asphyxia. Prolapse of the cord is an obstetric emergency.

Unless spontaneous delivery is imminent, the woman should be placed in the knee–chest position, or the buttocks elevated by pillows or head tilt in a trolley to reduce pressure on the cord. Filling the urinary bladder may help to reduce pressure on the cord by the presenting part. The cord should be digitally displaced into the vagina to maintain the warmth and moisture content and introitus covered with a wet pad. This is likely to reduce the incidence of cord arteral spasm. It is difficult to replace the cord into the uterus, although there has been a few reports about this possibility.

Vaginal examination and digital displacement of the head to alleviate pressure of the head on the cord is a possibility but it is difficult to transfer the woman to the theatre along the corridors with a hand in the vagina although she would be covered. Each uterine contraction may further compress the cord at the pelvic brim against the presenting part and a bolus dose of tocolytic (terbutaline 0.25 mg SC or slow IV in 5 mL saline) may be of help to relieve this intermittent compression.

Delivery should be effected by caesarean section unless the cervix is fully dilated and delivery can be achieved rapidly by forceps or vacuum with the assistance of the maternal expulsive efforts.

Despite the acute asphyxial insult to the fetus, which is likely to be depressed at birth, the long-term prognosis in these infants is good. Provided there is no pre-existing impairment to gaseous transfer, the fetus can effectively withstand an acute asphyxial episode without suffering long-term damage.